Systems comprising integrated circuits based on organic semiconductors, in particular organic field effect transistors (OFET), constitute a promising technology in the mass application sector of economical electronics. A field effect transistor is considered to be organic particularly if the semiconducting layer is produced from an organic material.
Since it is possible to build up complex circuits using OFETs, there are numerous potential applications. Thus, for example, the introduction of RF-ID (RF-ID: radio frequency identification) systems based on this technology is considered as a potential replacement for the bar code, which is susceptible to faults and can be used only in direct visual contact with the scanner.
In particular, circuits on flexible substrates, which can be produced in large quantities in roll-to-roll processes, are of interest here.
Owing to the thermal distortion of most suitable economical substrates (e.g. polyethylene terephthalate (PET), polyethylene naphthalate (PEN)), there is an upper temperature limit of 130-150° C. for the production of such flexible substrates. Under certain preconditions, for example a thermal pretreatment of the substrate, this temperature limit can be increased to 200° C. but with the restriction that, although the distortion of the substrate is reduced, it is not prevented.
A critical process step in the case of electronic components is the deposition of the dielectric layer, in particular the gate dielectric layer, of an OFET. The quality of the dielectrics in OFETs has to meet very high requirements with regard to the thermal, chemical, mechanical and electrical properties.
Silicon dioxide (SiO2) is the currently most frequently used gate dielectric in OFETs, based on the wide availability in semiconductor technology. Thus, transistor structures in which a doped silicon wafer serves as the gate electrode, and thermal SiO2 grown thereon forms the gate dielectric are described. This SiO2 is produced at temperatures of about 800-1000° C. Other processes (e.g. CVD) for the deposition of SiO2 on various substrates likewise operate at temperatures above 400° C. A group at PennState University has developed a process (ion beam sputtering) which makes it possible to deposit a high-quality SiO2 at process temperatures of 80° C. This is described in the articles by C. D. Sheraw, J. A. Nichols, D. J. Gunlach, J. R. Huang, C. C. Kuo, H. Klauk, T. N. Jackson, M. G. Kane, J. Campi, F. P. Cuomo and B. K. Greening, Techn. Dig.-lot. Electron Devices Meet., 619 (2000), and C. D. Sheraw, L. Zhou, J. R. Huang, D. J. Gundlach, T. N. Jackson, M. G. Kane, I. G. Hili, M. S. Hammond, J. Campi, B. K. Greening, J. Francl and J. West, Appl. Phys. Lett. 80, 1088 (2002).
However, the high process costs and the low throughput are disadvantageous here for mass-produced products.
It is also known that inorganic nitrides, such as, for example, SiNx′, TaNx, can be used. Similarly to the preparation of inorganic oxides, the deposits of inorganic nitrides require high temperatures or high process costs. This is described, for example, in the article by B. K. Crone, A. Dodabalapur, R. Sarpeshkar, R. W. Filas, Y. Y. Lin, Z. Bao, J. H. O'Neill, W. Li and H. E. Katz, J. Appl. Phys. 89, 5125 (2001).
It is also known that hybrid solutions (spin on glass) can be used. Organic siloxanes which can be prepared from a solution and can be converted into “glass-like” layers by thermal conversion were described. The conversion into SiO2 is effected either at high temperatures (about 400° C.) or takes place only partly, which results in a reduced transistor quality (in this context, cf. the article by Z. Bao, V. Kuck, J. A. Rogers and M. A. Paczkowski, Adv. Funct. Mater., 12, 526 (2002).
In addition, organic polymers, such as, for example, poly-4-vinylphenol (PVP), poly-4-vinylphenol-co-2-hydroxyethyl methacrylate or polyimide (PI), have already been used. These polymers are distinguished by their comparatively simple processability. Thus, they can be used, for example, from solution for spin coating or printing. The outstanding dielectric properties of such materials have already been demonstrated (cf. article by H. Klauk, M. Halik, U. Zschieschang, G. Schmid, W. Radlik and W. Weber, J. Appl. Phys., vol. 92, no. 9, 2002, p. 5259-5263).
It has also already been possible to demonstrate applications in interconnect layers (ICs), the required chemical and mechanical stabilities of the dielectric layers for the structuring thereof and the structuring of the subsequent source-drain layer having been achieved by crosslinking of the polymers (cf. article by M. Halik, H. Klauk, U. Zschieschang, T. Kriem, G. Schmid and W. Radlik, Appl. Phys. Lett., 81, 289 (2002)). However, this crosslinking is effected at temperatures of 200° C., which is problematic for the production of flexible substrates having a large area.